// SmallVector 是 std::vector 的替代，针对数组比较小的情况进行优化，但对大数组的表现也很好
// 相比 std::vector 有几点优势:
// 1. 数据较少时没有堆分配
// 2. 没有强异常保证，因此某些情况下更快
// 3. 对于 POD 类型直接操作内存而不是使用啰嗦且低效的 Allocator
// 移植自 https://github.com/llvm/llvm-project/blob/a6eddf9a79709e3161d3aad86d44ab1097f57f22/llvm/include/llvm/ADT/SmallVector.h 和 https://github.com/llvm/llvm-project/blob/a6eddf9a79709e3161d3aad86d44ab1097f57f22/llvm/lib/Support/SmallVector.cpp
// 所作修改如下:
// 1. 删除跨编译器逻辑
// 2. 修复 MSVC 警告


//===- llvm/ADT/SmallVector.h - 'Normally small' vectors --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file defines the SmallVector class.
 ///
 //===----------------------------------------------------------------------===//

#pragma once
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <initializer_list>
#include <iterator>
#include <limits>
#include <memory>
#include <new>
#include <type_traits>
#include <utility>


template <class Iterator>
using EnableIfConvertibleToInputIterator = std::enable_if_t<std::is_convertible<
	typename std::iterator_traits<Iterator>::iterator_category,
	std::input_iterator_tag>::value>;

/// This is all the stuff common to all SmallVectors.
///
/// The template parameter specifies the type which should be used to hold the
/// Size and Capacity of the SmallVector, so it can be adjusted.
/// Using 32 bit size is desirable to shrink the size of the SmallVector.
/// Using 64 bit size is desirable for cases like SmallVector<char>, where a
/// 32 bit size would limit the vector to ~4GB. SmallVectors are used for
/// buffering bitcode output - which can exceed 4GB.
template <class Size_T> class SmallVectorBase {
protected:
	void* BeginX;
	Size_T Size = 0, Capacity;

	/// The maximum value of the Size_T used.
	static constexpr size_t SizeTypeMax() {
		return std::numeric_limits<Size_T>::max();
	}

	SmallVectorBase() = delete;
	SmallVectorBase(void* FirstEl, size_t TotalCapacity)
		: BeginX(FirstEl), Capacity(static_cast<Size_T>(TotalCapacity)) {
	}

	/// This is a helper for \a grow() that's out of line to reduce code
	/// duplication.  This function will report a fatal error if it can't grow at
	/// least to \p MinSize.
	void* mallocForGrow(void* FirstEl, size_t MinSize, size_t TSize,
		size_t& NewCapacity);

	/// This is an implementation of the grow() method which only works
	/// on POD-like data types and is out of line to reduce code duplication.
	/// This function will report a fatal error if it cannot increase capacity.
	void grow_pod(void* FirstEl, size_t MinSize, size_t TSize);

	/// If vector was first created with capacity 0, getFirstEl() points to the
	/// memory right after, an area unallocated. If a subsequent allocation,
	/// that grows the vector, happens to return the same pointer as getFirstEl(),
	/// get a new allocation, otherwise isSmall() will falsely return that no
	/// allocation was done (true) and the memory will not be freed in the
	/// destructor. If a VSize is given (vector size), also copy that many
	/// elements to the new allocation - used if realloca fails to increase
	/// space, and happens to allocate precisely at BeginX.
	/// This is unlikely to be called often, but resolves a memory leak when the
	/// situation does occur.
	void* replaceAllocation(void* NewElts, size_t TSize, size_t NewCapacity,
		size_t VSize = 0);

public:
	size_t size() const { return Size; }
	size_t capacity() const { return Capacity; }

	[[nodiscard]] bool empty() const { return !Size; }

protected:
	/// Set the array size to \p N, which the current array must have enough
	/// capacity for.
	///
	/// This does not construct or destroy any elements in the vector.
	void set_size(size_t N) {
		assert(N <= capacity()); // implies no overflow in assignment
		Size = static_cast<Size_T>(N);
	}

	/// Set the array data pointer to \p Begin and capacity to \p N.
	///
	/// This does not construct or destroy any elements in the vector.
	//  This does not clean up any existing allocation.
	void set_allocation_range(void* Begin, size_t N) {
		assert(N <= SizeTypeMax());
		BeginX = Begin;
		Capacity = static_cast<Size_T>(N);
	}
};

template <class T>
using SmallVectorSizeType = std::conditional_t<sizeof(T) < 4 && sizeof(void*) >= 8, uint64_t, uint32_t>;

/// Figure out the offset of the first element.
template <class T, typename = void> struct SmallVectorAlignmentAndSize {
	alignas(SmallVectorBase<SmallVectorSizeType<T>>) char Base[sizeof(
		SmallVectorBase<SmallVectorSizeType<T>>)];
	alignas(T) char FirstEl[sizeof(T)];
};

/// This is the part of SmallVectorTemplateBase which does not depend on whether
/// the type T is a POD. The extra dummy template argument is used by ArrayRef
/// to avoid unnecessarily requiring T to be complete.
template <typename T, typename = void>
class SmallVectorTemplateCommon
	: public SmallVectorBase<SmallVectorSizeType<T>> {
	using Base = SmallVectorBase<SmallVectorSizeType<T>>;

protected:
	/// Find the address of the first element.  For this pointer math to be valid
	/// with small-size of 0 for T with lots of alignment, it's important that
	/// SmallVectorStorage is properly-aligned even for small-size of 0.
	void* getFirstEl() const {
		return const_cast<void*>(reinterpret_cast<const void*>(
			reinterpret_cast<const char*>(this) +
			offsetof(SmallVectorAlignmentAndSize<T>, FirstEl)));
	}
	// Space after 'FirstEl' is clobbered, do not add any instance vars after it.

	SmallVectorTemplateCommon(size_t Size) : Base(getFirstEl(), Size) {}

	void grow_pod(size_t MinSize, size_t TSize) {
		Base::grow_pod(getFirstEl(), MinSize, TSize);
	}

	/// Return true if this is a smallvector which has not had dynamic
	/// memory allocated for it.
	bool isSmall() const { return this->BeginX == getFirstEl(); }

	/// Put this vector in a state of being small.
	void resetToSmall() {
		this->BeginX = getFirstEl();
		this->Size = this->Capacity = 0; // FIXME: Setting Capacity to 0 is suspect.
	}

	/// Return true if V is an internal reference to the given range.
	bool isReferenceToRange(const void* V, const void* First, const void* Last) const {
	  // Use std::less to avoid UB.
		std::less<> LessThan;
		return !LessThan(V, First) && LessThan(V, Last);
	}

	/// Return true if V is an internal reference to this vector.
	bool isReferenceToStorage(const void* V) const {
		return isReferenceToRange(V, this->begin(), this->end());
	}

	/// Return true if First and Last form a valid (possibly empty) range in this
	/// vector's storage.
	bool isRangeInStorage(const void* First, const void* Last) const {
	  // Use std::less to avoid UB.
		std::less<> LessThan;
		return !LessThan(First, this->begin()) && !LessThan(Last, First) &&
			!LessThan(this->end(), Last);
	}

	/// Return true unless Elt will be invalidated by resizing the vector to
	/// NewSize.
	bool isSafeToReferenceAfterResize(const void* Elt, size_t NewSize) {
	  // Past the end.
		if (!isReferenceToStorage(Elt)) [[likely]]
			return true;

		  // Return false if Elt will be destroyed by shrinking.
		if (NewSize <= this->size())
			return Elt < this->begin() + NewSize;

		  // Return false if we need to grow.
		return NewSize <= this->capacity();
	}

	/// Check whether Elt will be invalidated by resizing the vector to NewSize.
	void assertSafeToReferenceAfterResize([[maybe_unused]] const void* Elt, [[maybe_unused]] size_t NewSize) {
		assert(isSafeToReferenceAfterResize(Elt, NewSize) &&
			"Attempting to reference an element of the vector in an operation "
			"that invalidates it");
	}

	/// Check whether Elt will be invalidated by increasing the size of the
	/// vector by N.
	void assertSafeToAdd(const void* Elt, size_t N = 1) {
		this->assertSafeToReferenceAfterResize(Elt, this->size() + N);
	}

	/// Check whether any part of the range will be invalidated by clearing.
	void assertSafeToReferenceAfterClear(const T* From, const T* To) {
		if (From == To)
			return;
		this->assertSafeToReferenceAfterResize(From, 0);
		this->assertSafeToReferenceAfterResize(To - 1, 0);
	}
	template <
		class ItTy,
		std::enable_if_t<!std::is_same<std::remove_const_t<ItTy>, T*>::value,
		bool> = false>
	void assertSafeToReferenceAfterClear(ItTy, ItTy) {}

	/// Check whether any part of the range will be invalidated by growing.
	void assertSafeToAddRange(const T* From, const T* To) {
		if (From == To)
			return;
		this->assertSafeToAdd(From, To - From);
		this->assertSafeToAdd(To - 1, To - From);
	}
	template <
		class ItTy,
		std::enable_if_t<!std::is_same<std::remove_const_t<ItTy>, T*>::value,
		bool> = false>
	void assertSafeToAddRange(ItTy, ItTy) {}

	/// Reserve enough space to add one element, and return the updated element
	/// pointer in case it was a reference to the storage.
	template <class U>
	static const T* reserveForParamAndGetAddressImpl(U* This, const T& Elt,
		size_t N) {
		size_t NewSize = This->size() + N;
		if (NewSize <= This->capacity())  [[likely]]
			return &Elt;

		bool ReferencesStorage = false;
		int64_t Index = -1;
		if (!U::TakesParamByValue) {
			if (This->isReferenceToStorage(&Elt)) [[unlikely]] {
				ReferencesStorage = true;
				Index = &Elt - This->begin();
			}
		}
		This->grow(NewSize);
		return ReferencesStorage ? This->begin() + Index : &Elt;
	}

public:
	using size_type = size_t;
	using difference_type = ptrdiff_t;
	using value_type = T;
	using iterator = T*;
	using const_iterator = const T*;

	using const_reverse_iterator = std::reverse_iterator<const_iterator>;
	using reverse_iterator = std::reverse_iterator<iterator>;

	using reference = T&;
	using const_reference = const T&;
	using pointer = T*;
	using const_pointer = const T*;

	using Base::capacity;
	using Base::empty;
	using Base::size;

	// forward iterator creation methods.
	iterator begin() { return (iterator)this->BeginX; }
	const_iterator begin() const { return (const_iterator)this->BeginX; }
	iterator end() { return begin() + size(); }
	const_iterator end() const { return begin() + size(); }

	// reverse iterator creation methods.
	reverse_iterator rbegin() { return reverse_iterator(end()); }
	const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
	reverse_iterator rend() { return reverse_iterator(begin()); }
	const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }

	size_type size_in_bytes() const { return size() * sizeof(T); }
	size_type max_size() const {
		return std::min(this->SizeTypeMax(), size_type(-1) / sizeof(T));
	}

	size_t capacity_in_bytes() const { return capacity() * sizeof(T); }

	/// Return a pointer to the vector's buffer, even if empty().
	pointer data() { return pointer(begin()); }
	/// Return a pointer to the vector's buffer, even if empty().
	const_pointer data() const { return const_pointer(begin()); }

	reference operator[](size_type idx) {
		assert(idx < size());
		return begin()[idx];
	}
	const_reference operator[](size_type idx) const {
		assert(idx < size());
		return begin()[idx];
	}

	reference front() {
		assert(!empty());
		return begin()[0];
	}
	const_reference front() const {
		assert(!empty());
		return begin()[0];
	}

	reference back() {
		assert(!empty());
		return end()[-1];
	}
	const_reference back() const {
		assert(!empty());
		return end()[-1];
	}
};

/// SmallVectorTemplateBase<TriviallyCopyable = false> - This is where we put
/// method implementations that are designed to work with non-trivial T's.
///
/// We approximate is_trivially_copyable with trivial move/copy construction and
/// trivial destruction. While the standard doesn't specify that you're allowed
/// copy these types with memcpy, there is no way for the type to observe this.
/// This catches the important case of std::pair<POD, POD>, which is not
/// trivially assignable.
template <typename T, bool = (std::is_trivially_copy_constructible<T>::value) &&
	(std::is_trivially_move_constructible<T>::value) &&
	std::is_trivially_destructible<T>::value>
class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
	friend class SmallVectorTemplateCommon<T>;

protected:
	static constexpr bool TakesParamByValue = false;
	using ValueParamT = const T&;

	SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}

	static void destroy_range(T* S, T* E) {
		while (S != E) {
			--E;
			E->~T();
		}
	}

	/// Move the range [I, E) into the uninitialized memory starting with "Dest",
	/// constructing elements as needed.
	template<typename It1, typename It2>
	static void uninitialized_move(It1 I, It1 E, It2 Dest) {
		std::uninitialized_move(I, E, Dest);
	}

	/// Copy the range [I, E) onto the uninitialized memory starting with "Dest",
	/// constructing elements as needed.
	template<typename It1, typename It2>
	static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
		std::uninitialized_copy(I, E, Dest);
	}

	/// Grow the allocated memory (without initializing new elements), doubling
	/// the size of the allocated memory. Guarantees space for at least one more
	/// element, or MinSize more elements if specified.
	void grow(size_t MinSize = 0);

	/// Create a new allocation big enough for \p MinSize and pass back its size
	/// in \p NewCapacity. This is the first section of \a grow().
	T* mallocForGrow(size_t MinSize, size_t& NewCapacity);

	/// Move existing elements over to the new allocation \p NewElts, the middle
	/// section of \a grow().
	void moveElementsForGrow(T* NewElts);

	/// Transfer ownership of the allocation, finishing up \a grow().
	void takeAllocationForGrow(T* NewElts, size_t NewCapacity);

	/// Reserve enough space to add one element, and return the updated element
	/// pointer in case it was a reference to the storage.
	const T* reserveForParamAndGetAddress(const T& Elt, size_t N = 1) {
		return this->reserveForParamAndGetAddressImpl(this, Elt, N);
	}

	/// Reserve enough space to add one element, and return the updated element
	/// pointer in case it was a reference to the storage.
	T* reserveForParamAndGetAddress(T& Elt, size_t N = 1) {
		return const_cast<T*>(
			this->reserveForParamAndGetAddressImpl(this, Elt, N));
	}

	static T&& forward_value_param(T&& V) { return std::move(V); }
	static const T& forward_value_param(const T& V) { return V; }

	void growAndAssign(size_t NumElts, const T& Elt) {
		// Grow manually in case Elt is an internal reference.
		size_t NewCapacity;
		T* NewElts = mallocForGrow(NumElts, NewCapacity);
		std::uninitialized_fill_n(NewElts, NumElts, Elt);
		this->destroy_range(this->begin(), this->end());
		takeAllocationForGrow(NewElts, NewCapacity);
		this->set_size(NumElts);
	}

	template <typename... ArgTypes> T& growAndEmplaceBack(ArgTypes &&... Args) {
	  // Grow manually in case one of Args is an internal reference.
		size_t NewCapacity;
		T* NewElts = mallocForGrow(0, NewCapacity);
		::new ((void*)(NewElts + this->size())) T(std::forward<ArgTypes>(Args)...);
		moveElementsForGrow(NewElts);
		takeAllocationForGrow(NewElts, NewCapacity);
		this->set_size(this->size() + 1);
		return this->back();
	}

public:
	void push_back(const T& Elt) {
		const T* EltPtr = reserveForParamAndGetAddress(Elt);
		::new ((void*)this->end()) T(*EltPtr);
		this->set_size(this->size() + 1);
	}

	void push_back(T&& Elt) {
		T* EltPtr = reserveForParamAndGetAddress(Elt);
		::new ((void*)this->end()) T(::std::move(*EltPtr));
		this->set_size(this->size() + 1);
	}

	void pop_back() {
		this->set_size(this->size() - 1);
		this->end()->~T();
	}
};

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void SmallVectorTemplateBase<T, TriviallyCopyable>::grow(size_t MinSize) {
	size_t NewCapacity;
	T* NewElts = mallocForGrow(MinSize, NewCapacity);
	moveElementsForGrow(NewElts);
	takeAllocationForGrow(NewElts, NewCapacity);
}

template <typename T, bool TriviallyCopyable>
T* SmallVectorTemplateBase<T, TriviallyCopyable>::mallocForGrow(
	size_t MinSize, size_t& NewCapacity) {
	return static_cast<T*>(
		SmallVectorBase<SmallVectorSizeType<T>>::mallocForGrow(
		this->getFirstEl(), MinSize, sizeof(T), NewCapacity));
}

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void SmallVectorTemplateBase<T, TriviallyCopyable>::moveElementsForGrow(
	T* NewElts) {
	// Move the elements over.
	this->uninitialized_move(this->begin(), this->end(), NewElts);

	// Destroy the original elements.
	destroy_range(this->begin(), this->end());
}

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void SmallVectorTemplateBase<T, TriviallyCopyable>::takeAllocationForGrow(
	T* NewElts, size_t NewCapacity) {
	// If this wasn't grown from the inline copy, deallocate the old space.
	if (!this->isSmall())
		free(this->begin());

	this->set_allocation_range(NewElts, NewCapacity);
}

/// SmallVectorTemplateBase<TriviallyCopyable = true> - This is where we put
/// method implementations that are designed to work with trivially copyable
/// T's. This allows using memcpy in place of copy/move construction and
/// skipping destruction.
template <typename T>
class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
	friend class SmallVectorTemplateCommon<T>;

protected:
	/// True if it's cheap enough to take parameters by value. Doing so avoids
	/// overhead related to mitigations for reference invalidation.
	static constexpr bool TakesParamByValue = sizeof(T) <= 2 * sizeof(void*);

	/// Either const T& or T, depending on whether it's cheap enough to take
	/// parameters by value.
	using ValueParamT = std::conditional_t<TakesParamByValue, T, const T&>;

	SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}

	// No need to do a destroy loop for POD's.
	static void destroy_range(T*, T*) {}

	/// Move the range [I, E) onto the uninitialized memory
	/// starting with "Dest", constructing elements into it as needed.
	template<typename It1, typename It2>
	static void uninitialized_move(It1 I, It1 E, It2 Dest) {
		// Just do a copy.
		uninitialized_copy(I, E, Dest);
	}

	/// Copy the range [I, E) onto the uninitialized memory
	/// starting with "Dest", constructing elements into it as needed.
	template<typename It1, typename It2>
	static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
		// Arbitrary iterator types; just use the basic implementation.
		std::uninitialized_copy(I, E, Dest);
	}

	/// Copy the range [I, E) onto the uninitialized memory
	/// starting with "Dest", constructing elements into it as needed.
	template <typename T1, typename T2>
	static void uninitialized_copy(
		T1* I, T1* E, T2* Dest,
		std::enable_if_t<std::is_same<std::remove_const_t<T1>, T2>::value>* =
		nullptr) {
		// Use memcpy for PODs iterated by pointers (which includes SmallVector
		// iterators): std::uninitialized_copy optimizes to memmove, but we can
		// use memcpy here. Note that I and E are iterators and thus might be
		// invalid for memcpy if they are equal.
		if (I != E)
			memcpy(reinterpret_cast<void*>(Dest), I, (E - I) * sizeof(T));
	}

	/// Double the size of the allocated memory, guaranteeing space for at
	/// least one more element or MinSize if specified.
	void grow(size_t MinSize = 0) { this->grow_pod(MinSize, sizeof(T)); }

	/// Reserve enough space to add one element, and return the updated element
	/// pointer in case it was a reference to the storage.
	const T* reserveForParamAndGetAddress(const T& Elt, size_t N = 1) {
		return this->reserveForParamAndGetAddressImpl(this, Elt, N);
	}

	/// Reserve enough space to add one element, and return the updated element
	/// pointer in case it was a reference to the storage.
	T* reserveForParamAndGetAddress(T& Elt, size_t N = 1) {
		return const_cast<T*>(
			this->reserveForParamAndGetAddressImpl(this, Elt, N));
	}

	/// Copy \p V or return a reference, depending on \a ValueParamT.
	static ValueParamT forward_value_param(ValueParamT V) { return V; }

	void growAndAssign(size_t NumElts, T Elt) {
		// Elt has been copied in case it's an internal reference, side-stepping
		// reference invalidation problems without losing the realloc optimization.
		this->set_size(0);
		this->grow(NumElts);
		std::uninitialized_fill_n(this->begin(), NumElts, Elt);
		this->set_size(NumElts);
	}

	template <typename... ArgTypes> T& growAndEmplaceBack(ArgTypes &&... Args) {
		// Use push_back with a copy in case Args has an internal reference,
		// side-stepping reference invalidation problems without losing the realloc
		// optimization.
		push_back(T(std::forward<ArgTypes>(Args)...));
		return this->back();
	}

public:
	void push_back(ValueParamT Elt) {
		const T* EltPtr = reserveForParamAndGetAddress(Elt);
		memcpy(reinterpret_cast<void*>(this->end()), EltPtr, sizeof(T));
		this->set_size(this->size() + 1);
	}

	void pop_back() { this->set_size(this->size() - 1); }
};

/// This class consists of common code factored out of the SmallVector class to
/// reduce code duplication based on the SmallVector 'N' template parameter.
template <typename T>
class SmallVectorImpl : public SmallVectorTemplateBase<T> {
	using SuperClass = SmallVectorTemplateBase<T>;

public:
	using iterator = typename SuperClass::iterator;
	using const_iterator = typename SuperClass::const_iterator;
	using reference = typename SuperClass::reference;
	using size_type = typename SuperClass::size_type;

protected:
	using SmallVectorTemplateBase<T>::TakesParamByValue;
	using ValueParamT = typename SuperClass::ValueParamT;

	// Default ctor - Initialize to empty.
	explicit SmallVectorImpl(unsigned N)
		: SmallVectorTemplateBase<T>(N) {}

	void assignRemote(SmallVectorImpl&& RHS) {
		this->destroy_range(this->begin(), this->end());
		if (!this->isSmall())
			free(this->begin());
		this->BeginX = RHS.BeginX;
		this->Size = RHS.Size;
		this->Capacity = RHS.Capacity;
		RHS.resetToSmall();
	}

	~SmallVectorImpl() {
		// Subclass has already destructed this vector's elements.
		// If this wasn't grown from the inline copy, deallocate the old space.
		if (!this->isSmall())
			free(this->begin());
	}

public:
	SmallVectorImpl(const SmallVectorImpl&) = delete;

	void clear() {
		this->destroy_range(this->begin(), this->end());
		this->Size = 0;
	}

private:
	// Make set_size() private to avoid misuse in subclasses.
	using SuperClass::set_size;

	template <bool ForOverwrite> void resizeImpl(size_type N) {
		if (N == this->size())
			return;

		if (N < this->size()) {
			this->truncate(N);
			return;
		}

		this->reserve(N);
		for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
			if (ForOverwrite)
				new (&*I) T;
			else
				new (&*I) T();
		this->set_size(N);
	}

public:
	void resize(size_type N) { resizeImpl<false>(N); }

	/// Like resize, but \ref T is POD, the new values won't be initialized.
	void resize_for_overwrite(size_type N) { resizeImpl<true>(N); }

	/// Like resize, but requires that \p N is less than \a size().
	void truncate(size_type N) {
		assert(this->size() >= N && "Cannot increase size with truncate");
		this->destroy_range(this->begin() + N, this->end());
		this->set_size(N);
	}

	void resize(size_type N, ValueParamT NV) {
		if (N == this->size())
			return;

		if (N < this->size()) {
			this->truncate(N);
			return;
		}

		// N > this->size(). Defer to append.
		this->append(N - this->size(), NV);
	}

	void reserve(size_type N) {
		if (this->capacity() < N)
			this->grow(N);
	}

	void pop_back_n(size_type NumItems) {
		assert(this->size() >= NumItems);
		truncate(this->size() - NumItems);
	}

	[[nodiscard]] T pop_back_val() {
		T Result = ::std::move(this->back());
		this->pop_back();
		return Result;
	}

	void swap(SmallVectorImpl& RHS);

	/// Add the specified range to the end of the SmallVector.
	template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
	void append(ItTy in_start, ItTy in_end) {
		this->assertSafeToAddRange(in_start, in_end);
		size_type NumInputs = std::distance(in_start, in_end);
		this->reserve(this->size() + NumInputs);
		this->uninitialized_copy(in_start, in_end, this->end());
		this->set_size(this->size() + NumInputs);
	}

	/// Append \p NumInputs copies of \p Elt to the end.
	void append(size_type NumInputs, ValueParamT Elt) {
		const T* EltPtr = this->reserveForParamAndGetAddress(Elt, NumInputs);
		std::uninitialized_fill_n(this->end(), NumInputs, *EltPtr);
		this->set_size(this->size() + NumInputs);
	}

	void append(std::initializer_list<T> IL) {
		append(IL.begin(), IL.end());
	}

	void append(const SmallVectorImpl& RHS) { append(RHS.begin(), RHS.end()); }

	void assign(size_type NumElts, ValueParamT Elt) {
		// Note that Elt could be an internal reference.
		if (NumElts > this->capacity()) {
			this->growAndAssign(NumElts, Elt);
			return;
		}

		// Assign over existing elements.
		std::fill_n(this->begin(), std::min(NumElts, this->size()), Elt);
		if (NumElts > this->size())
			std::uninitialized_fill_n(this->end(), NumElts - this->size(), Elt);
		else if (NumElts < this->size())
			this->destroy_range(this->begin() + NumElts, this->end());
		this->set_size(NumElts);
	}

	// FIXME: Consider assigning over existing elements, rather than clearing &
	// re-initializing them - for all assign(...) variants.

	template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
	void assign(ItTy in_start, ItTy in_end) {
		this->assertSafeToReferenceAfterClear(in_start, in_end);
		clear();
		append(in_start, in_end);
	}

	void assign(std::initializer_list<T> IL) {
		clear();
		append(IL);
	}

	void assign(const SmallVectorImpl& RHS) { assign(RHS.begin(), RHS.end()); }

	iterator erase(const_iterator CI) {
		// Just cast away constness because this is a non-const member function.
		iterator I = const_cast<iterator>(CI);

		assert(this->isReferenceToStorage(CI) && "Iterator to erase is out of bounds.");

		iterator N = I;
		// Shift all elts down one.
		std::move(I + 1, this->end(), I);
		// Drop the last elt.
		this->pop_back();
		return(N);
	}

	iterator erase(const_iterator CS, const_iterator CE) {
		// Just cast away constness because this is a non-const member function.
		iterator S = const_cast<iterator>(CS);
		iterator E = const_cast<iterator>(CE);

		assert(this->isRangeInStorage(S, E) && "Range to erase is out of bounds.");

		iterator N = S;
		// Shift all elts down.
		iterator I = std::move(E, this->end(), S);
		// Drop the last elts.
		this->destroy_range(I, this->end());
		this->set_size(I - this->begin());
		return(N);
	}

private:
	template <class ArgType> iterator insert_one_impl(iterator I, ArgType&& Elt) {
		// Callers ensure that ArgType is derived from T.
		static_assert(
			std::is_same<std::remove_const_t<std::remove_reference_t<ArgType>>,
			T>::value,
			"ArgType must be derived from T!");

		if (I == this->end()) {  // Important special case for empty vector.
			this->push_back(::std::forward<ArgType>(Elt));
			return this->end() - 1;
		}

		assert(this->isReferenceToStorage(I) && "Insertion iterator is out of bounds.");

		// Grow if necessary.
		size_t Index = I - this->begin();
		std::remove_reference_t<ArgType>* EltPtr =
			this->reserveForParamAndGetAddress(Elt);
		I = this->begin() + Index;

		::new ((void*)this->end()) T(::std::move(this->back()));
		// Push everything else over.
		std::move_backward(I, this->end() - 1, this->end());
		this->set_size(this->size() + 1);

		// If we just moved the element we're inserting, be sure to update
		// the reference (never happens if TakesParamByValue).
		static_assert(!TakesParamByValue || std::is_same<ArgType, T>::value,
			"ArgType must be 'T' when taking by value!");
		if (!TakesParamByValue && this->isReferenceToRange(EltPtr, I, this->end()))
			++EltPtr;

		*I = ::std::forward<ArgType>(*EltPtr);
		return I;
	}

public:
	iterator insert(iterator I, T&& Elt) {
		return insert_one_impl(I, this->forward_value_param(std::move(Elt)));
	}

	iterator insert(iterator I, const T& Elt) {
		return insert_one_impl(I, this->forward_value_param(Elt));
	}

	iterator insert(iterator I, size_type NumToInsert, ValueParamT Elt) {
		// Convert iterator to elt# to avoid invalidating iterator when we reserve()
		size_t InsertElt = I - this->begin();

		if (I == this->end()) {  // Important special case for empty vector.
			append(NumToInsert, Elt);
			return this->begin() + InsertElt;
		}

		assert(this->isReferenceToStorage(I) && "Insertion iterator is out of bounds.");

		// Ensure there is enough space, and get the (maybe updated) address of
		// Elt.
		const T* EltPtr = this->reserveForParamAndGetAddress(Elt, NumToInsert);

		// Uninvalidate the iterator.
		I = this->begin() + InsertElt;

		// If there are more elements between the insertion point and the end of the
		// range than there are being inserted, we can use a simple approach to
		// insertion.  Since we already reserved space, we know that this won't
		// reallocate the vector.
		if (size_t(this->end() - I) >= NumToInsert) {
			T* OldEnd = this->end();
			append(std::move_iterator<iterator>(this->end() - NumToInsert),
				std::move_iterator<iterator>(this->end()));

		 // Copy the existing elements that get replaced.
			std::move_backward(I, OldEnd - NumToInsert, OldEnd);

			// If we just moved the element we're inserting, be sure to update
			// the reference (never happens if TakesParamByValue).
			if (!TakesParamByValue && I <= EltPtr && EltPtr < this->end())
				EltPtr += NumToInsert;

			std::fill_n(I, NumToInsert, *EltPtr);
			return I;
		}

		// Otherwise, we're inserting more elements than exist already, and we're
		// not inserting at the end.

		// Move over the elements that we're about to overwrite.
		T* OldEnd = this->end();
		this->set_size(this->size() + NumToInsert);
		size_t NumOverwritten = OldEnd - I;
		this->uninitialized_move(I, OldEnd, this->end() - NumOverwritten);

		// If we just moved the element we're inserting, be sure to update
		// the reference (never happens if TakesParamByValue).
		if (!TakesParamByValue && I <= EltPtr && EltPtr < this->end())
			EltPtr += NumToInsert;

		  // Replace the overwritten part.
		std::fill_n(I, NumOverwritten, *EltPtr);

		// Insert the non-overwritten middle part.
		std::uninitialized_fill_n(OldEnd, NumToInsert - NumOverwritten, *EltPtr);
		return I;
	}

	template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
	iterator insert(iterator I, ItTy From, ItTy To) {
		// Convert iterator to elt# to avoid invalidating iterator when we reserve()
		size_t InsertElt = I - this->begin();

		if (I == this->end()) {  // Important special case for empty vector.
			append(From, To);
			return this->begin() + InsertElt;
		}

		assert(this->isReferenceToStorage(I) && "Insertion iterator is out of bounds.");

		// Check that the reserve that follows doesn't invalidate the iterators.
		this->assertSafeToAddRange(From, To);

		size_t NumToInsert = std::distance(From, To);

		// Ensure there is enough space.
		reserve(this->size() + NumToInsert);

		// Uninvalidate the iterator.
		I = this->begin() + InsertElt;

		// If there are more elements between the insertion point and the end of the
		// range than there are being inserted, we can use a simple approach to
		// insertion.  Since we already reserved space, we know that this won't
		// reallocate the vector.
		if (size_t(this->end() - I) >= NumToInsert) {
			T* OldEnd = this->end();
			append(std::move_iterator<iterator>(this->end() - NumToInsert),
				std::move_iterator<iterator>(this->end()));

			// Copy the existing elements that get replaced.
			std::move_backward(I, OldEnd - NumToInsert, OldEnd);

			std::copy(From, To, I);
			return I;
		}

		// Otherwise, we're inserting more elements than exist already, and we're
		// not inserting at the end.

		// Move over the elements that we're about to overwrite.
		T* OldEnd = this->end();
		this->set_size(this->size() + NumToInsert);
		size_t NumOverwritten = OldEnd - I;
		this->uninitialized_move(I, OldEnd, this->end() - NumOverwritten);

		// Replace the overwritten part.
		for (T* J = I; NumOverwritten > 0; --NumOverwritten) {
			*J = *From;
			++J; ++From;
		}

		// Insert the non-overwritten middle part.
		this->uninitialized_copy(From, To, OldEnd);
		return I;
	}

	void insert(iterator I, std::initializer_list<T> IL) {
		insert(I, IL.begin(), IL.end());
	}

	template <typename... ArgTypes> reference emplace_back(ArgTypes &&... Args) {
		if (this->size() >= this->capacity()) [[unlikely]]
			return this->growAndEmplaceBack(std::forward<ArgTypes>(Args)...);

		::new ((void*)this->end()) T(std::forward<ArgTypes>(Args)...);
		this->set_size(this->size() + 1);
		return this->back();
	}

	SmallVectorImpl& operator=(const SmallVectorImpl& RHS);

	SmallVectorImpl& operator=(SmallVectorImpl&& RHS) noexcept;

	bool operator==(const SmallVectorImpl& RHS) const {
		if (this->size() != RHS.size()) return false;
		return std::equal(this->begin(), this->end(), RHS.begin());
	}
	bool operator!=(const SmallVectorImpl& RHS) const {
		return !(*this == RHS);
	}

	bool operator<(const SmallVectorImpl& RHS) const {
		return std::lexicographical_compare(this->begin(), this->end(),
			RHS.begin(), RHS.end());
	}
	bool operator>(const SmallVectorImpl& RHS) const { return RHS < *this; }
	bool operator<=(const SmallVectorImpl& RHS) const { return !(*this > RHS); }
	bool operator>=(const SmallVectorImpl& RHS) const { return !(*this < RHS); }
};

template <typename T>
void SmallVectorImpl<T>::swap(SmallVectorImpl<T>& RHS) {
	if (this == &RHS) return;

	// We can only avoid copying elements if neither vector is small.
	if (!this->isSmall() && !RHS.isSmall()) {
		std::swap(this->BeginX, RHS.BeginX);
		std::swap(this->Size, RHS.Size);
		std::swap(this->Capacity, RHS.Capacity);
		return;
	}
	this->reserve(RHS.size());
	RHS.reserve(this->size());

	// Swap the shared elements.
	size_t NumShared = this->size();
	if (NumShared > RHS.size()) NumShared = RHS.size();
	for (size_type i = 0; i != NumShared; ++i)
		std::swap((*this)[i], RHS[i]);

	// Copy over the extra elts.
	if (this->size() > RHS.size()) {
		size_t EltDiff = this->size() - RHS.size();
		this->uninitialized_copy(this->begin() + NumShared, this->end(), RHS.end());
		RHS.set_size(RHS.size() + EltDiff);
		this->destroy_range(this->begin() + NumShared, this->end());
		this->set_size(NumShared);
	} else if (RHS.size() > this->size()) {
		size_t EltDiff = RHS.size() - this->size();
		this->uninitialized_copy(RHS.begin() + NumShared, RHS.end(), this->end());
		this->set_size(this->size() + EltDiff);
		this->destroy_range(RHS.begin() + NumShared, RHS.end());
		RHS.set_size(NumShared);
	}
}

template <typename T>
SmallVectorImpl<T>& SmallVectorImpl<T>::
operator=(const SmallVectorImpl<T>& RHS) {
	// Avoid self-assignment.
	if (this == &RHS) return *this;

	// If we already have sufficient space, assign the common elements, then
	// destroy any excess.
	size_t RHSSize = RHS.size();
	size_t CurSize = this->size();
	if (CurSize >= RHSSize) {
		// Assign common elements.
		iterator NewEnd;
		if (RHSSize)
			NewEnd = std::copy(RHS.begin(), RHS.begin() + RHSSize, this->begin());
		else
			NewEnd = this->begin();

		// Destroy excess elements.
		this->destroy_range(NewEnd, this->end());

		// Trim.
		this->set_size(RHSSize);
		return *this;
	}

	// If we have to grow to have enough elements, destroy the current elements.
	// This allows us to avoid copying them during the grow.
	// FIXME: don't do this if they're efficiently moveable.
	if (this->capacity() < RHSSize) {
		// Destroy current elements.
		this->clear();
		CurSize = 0;
		this->grow(RHSSize);
	} else if (CurSize) {
		// Otherwise, use assignment for the already-constructed elements.
		std::copy(RHS.begin(), RHS.begin() + CurSize, this->begin());
	}

	// Copy construct the new elements in place.
	this->uninitialized_copy(RHS.begin() + CurSize, RHS.end(),
		this->begin() + CurSize);

	// Set end.
	this->set_size(RHSSize);
	return *this;
}

template <typename T>
SmallVectorImpl<T>& SmallVectorImpl<T>::operator=(SmallVectorImpl<T>&& RHS) noexcept {
	// Avoid self-assignment.
	if (this == &RHS) return *this;

	// If the RHS isn't small, clear this vector and then steal its buffer.
	if (!RHS.isSmall()) {
		this->assignRemote(std::move(RHS));
		return *this;
	}

	// If we already have sufficient space, assign the common elements, then
	// destroy any excess.
	size_t RHSSize = RHS.size();
	size_t CurSize = this->size();
	if (CurSize >= RHSSize) {
		// Assign common elements.
		iterator NewEnd = this->begin();
		if (RHSSize)
			NewEnd = std::move(RHS.begin(), RHS.end(), NewEnd);

		// Destroy excess elements and trim the bounds.
		this->destroy_range(NewEnd, this->end());
		this->set_size(RHSSize);

		// Clear the RHS.
		RHS.clear();

		return *this;
	}

	// If we have to grow to have enough elements, destroy the current elements.
	// This allows us to avoid copying them during the grow.
	// FIXME: this may not actually make any sense if we can efficiently move
	// elements.
	if (this->capacity() < RHSSize) {
		// Destroy current elements.
		this->clear();
		CurSize = 0;
		this->grow(RHSSize);
	} else if (CurSize) {
		// Otherwise, use assignment for the already-constructed elements.
		std::move(RHS.begin(), RHS.begin() + CurSize, this->begin());
	}

	// Move-construct the new elements in place.
	this->uninitialized_move(RHS.begin() + CurSize, RHS.end(),
		this->begin() + CurSize);

	// Set end.
	this->set_size(RHSSize);

	RHS.clear();
	return *this;
}

/// Storage for the SmallVector elements.  This is specialized for the N=0 case
/// to avoid allocating unnecessary storage.
template <typename T, unsigned N>
struct SmallVectorStorage {
	alignas(T) char InlineElts[N * sizeof(T)];
};

#pragma warning(push)
#pragma warning(disable: 4324)  // “SmallVectorStorage<T,0>”: 由于对齐说明符，结构被填充
/// We need the storage to be properly aligned even for small-size of 0 so that
/// the pointer math in \a SmallVectorTemplateCommon::getFirstEl() is
/// well-defined.
template <typename T> struct alignas(T) SmallVectorStorage<T, 0> {};
#pragma warning(pop)

/// Forward declaration of SmallVector so that
/// calculateSmallVectorDefaultInlinedElements can reference
/// `sizeof(SmallVector<T, 0>)`.
template <typename T, unsigned N> class SmallVector;

/// Helper class for calculating the default number of inline elements for
/// `SmallVector<T>`.
///
/// This should be migrated to a constexpr function when our minimum
/// compiler support is enough for multi-statement constexpr functions.
template <typename T> struct CalculateSmallVectorDefaultInlinedElements {
  // Parameter controlling the default number of inlined elements
  // for `SmallVector<T>`.
  //
  // The default number of inlined elements ensures that
  // 1. There is at least one inlined element.
  // 2. `sizeof(SmallVector<T>) <= kPreferredSmallVectorSizeof` unless
  // it contradicts 1.
	static constexpr size_t kPreferredSmallVectorSizeof = 64;

	// static_assert that sizeof(T) is not "too big".
	//
	// Because our policy guarantees at least one inlined element, it is possible
	// for an arbitrarily large inlined element to allocate an arbitrarily large
	// amount of inline storage. We generally consider it an antipattern for a
	// SmallVector to allocate an excessive amount of inline storage, so we want
	// to call attention to these cases and make sure that users are making an
	// intentional decision if they request a lot of inline storage.
	//
	// We want this assertion to trigger in pathological cases, but otherwise
	// not be too easy to hit. To accomplish that, the cutoff is actually somewhat
	// larger than kPreferredSmallVectorSizeof (otherwise,
	// `SmallVector<SmallVector<T>>` would be one easy way to trip it, and that
	// pattern seems useful in practice).
	//
	// One wrinkle is that this assertion is in theory non-portable, since
	// sizeof(T) is in general platform-dependent. However, we don't expect this
	// to be much of an issue, because most LLVM development happens on 64-bit
	// hosts, and therefore sizeof(T) is expected to *decrease* when compiled for
	// 32-bit hosts, dodging the issue. The reverse situation, where development
	// happens on a 32-bit host and then fails due to sizeof(T) *increasing* on a
	// 64-bit host, is expected to be very rare.
	static_assert(
		sizeof(T) <= 256,
		"You are trying to use a default number of inlined elements for "
		"`SmallVector<T>` but `sizeof(T)` is really big! Please use an "
		"explicit number of inlined elements with `SmallVector<T, N>` to make "
		"sure you really want that much inline storage.");

	// Discount the size of the header itself when calculating the maximum inline
	// bytes.
	static constexpr size_t PreferredInlineBytes =
		kPreferredSmallVectorSizeof - sizeof(SmallVector<T, 0>);
	static constexpr size_t NumElementsThatFit = PreferredInlineBytes / sizeof(T);
	static constexpr size_t value =
		NumElementsThatFit == 0 ? 1 : NumElementsThatFit;
};

/// This is a 'vector' (really, a variable-sized array), optimized
/// for the case when the array is small.  It contains some number of elements
/// in-place, which allows it to avoid heap allocation when the actual number of
/// elements is below that threshold.  This allows normal "small" cases to be
/// fast without losing generality for large inputs.
///
/// \note
/// In the absence of a well-motivated choice for the number of inlined
/// elements \p N, it is recommended to use \c SmallVector<T> (that is,
/// omitting the \p N). This will choose a default number of inlined elements
/// reasonable for allocation on the stack (for example, trying to keep \c
/// sizeof(SmallVector<T>) around 64 bytes).
///
/// \warning This does not attempt to be exception safe.
///
/// \see https://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallvector-h
template <typename T,
	unsigned N = CalculateSmallVectorDefaultInlinedElements<T>::value>
class SmallVector : public SmallVectorImpl<T>,
	SmallVectorStorage<T, N> {
public:
	SmallVector() : SmallVectorImpl<T>(N) {}

	~SmallVector() {
		// Destroy the constructed elements in the vector.
		this->destroy_range(this->begin(), this->end());
	}

	explicit SmallVector(size_t Size)
		: SmallVectorImpl<T>(N) {
		this->resize(Size);
	}

	SmallVector(size_t Size, const T& Value)
		: SmallVectorImpl<T>(N) {
		this->assign(Size, Value);
	}

	template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
	SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(N) {
		this->append(S, E);
	}

	SmallVector(std::initializer_list<T> IL) : SmallVectorImpl<T>(N) {
		this->append(IL);
	}

	SmallVector(const SmallVector& RHS) : SmallVectorImpl<T>(N) {
		if (!RHS.empty())
			SmallVectorImpl<T>::operator=(RHS);
	}

	SmallVector& operator=(const SmallVector& RHS) {
		SmallVectorImpl<T>::operator=(RHS);
		return *this;
	}

	SmallVector(SmallVector&& RHS) noexcept : SmallVectorImpl<T>(N) {
		if (!RHS.empty())
			SmallVectorImpl<T>::operator=(::std::move(RHS));
	}

	SmallVector(SmallVectorImpl<T>&& RHS) : SmallVectorImpl<T>(N) {
		if (!RHS.empty())
			SmallVectorImpl<T>::operator=(::std::move(RHS));
	}

	SmallVector& operator=(SmallVector&& RHS) {
		if constexpr (N) {
			SmallVectorImpl<T>::operator=(::std::move(RHS));
		} else {
			// SmallVectorImpl<T>::operator= does not leverage N==0. Optimize the case.
			if (this == &RHS)
				return *this;
			if (RHS.empty()) {
				this->destroy_range(this->begin(), this->end());
				this->Size = 0;
			} else {
				this->assignRemote(std::move(RHS));
			}
		}

		return *this;
	}

	SmallVector& operator=(SmallVectorImpl<T>&& RHS) {
		SmallVectorImpl<T>::operator=(::std::move(RHS));
		return *this;
	}

	SmallVector& operator=(std::initializer_list<T> IL) {
		this->assign(IL);
		return *this;
	}
};

template <typename T, unsigned N>
inline size_t capacity_in_bytes(const SmallVector<T, N>& X) {
	return X.capacity_in_bytes();
}

template <typename RangeType>
using ValueTypeFromRangeType =
std::remove_const_t<std::remove_reference_t<decltype(*std::begin(
	std::declval<RangeType&>()))>>;

/// Given a range of type R, iterate the entire range and return a
/// SmallVector with elements of the vector.  This is useful, for example,
/// when you want to iterate a range and then sort the results.
template <unsigned Size, typename R>
SmallVector<ValueTypeFromRangeType<R>, Size> to_vector(R&& Range) {
	return { std::begin(Range), std::end(Range) };
}
template <typename R>
SmallVector<ValueTypeFromRangeType<R>> to_vector(R&& Range) {
	return { std::begin(Range), std::end(Range) };
}

template <typename Out, unsigned Size, typename R>
SmallVector<Out, Size> to_vector_of(R&& Range) {
	return { std::begin(Range), std::end(Range) };
}

template <typename Out, typename R> SmallVector<Out> to_vector_of(R&& Range) {
	return { std::begin(Range), std::end(Range) };
}


namespace std {

/// Implement std::swap in terms of SmallVector swap.
template<typename T>
inline void swap(SmallVectorImpl<T>& LHS, SmallVectorImpl<T>& RHS) {
	LHS.swap(RHS);
}

/// Implement std::swap in terms of SmallVector swap.
template<typename T, unsigned N>
inline void swap(SmallVector<T, N>& LHS, SmallVector<T, N>& RHS) {
	LHS.swap(RHS);
}

} // end namespace std
